The Best Gene

In the body it gets broken up into different proteins, including melanotropin, which makes the skin darker when you’ve been in the sun, and beta-endorphin, a natural opioid that makes you feel satisfied after eating and also causes the ‘runner’s high.’ It’s the only gene I know whose very structure is an implicit biological message: Happiness is a reward for doing what we should be doing—for being in the sun and making vitamin D, for exercising and for bringing nutrients into our bodies.